This invention relates generally to a tire building machine employing ply turn-up mechanisms or the like operatively associated with a tire building drum, and more particularly to such mechanisms which incorporate inflatable bladders to turn the edges of plies at the drum shoulders over onto themselves to encase inextensible bead rings previously positioned at the shoulders.
Many tire building machines presently in use include ply turn-up mechanisms incorporating one or two expansible cooperating air bags or bladders which when brought into proper position at the end of a tire building drum and inflated cause the previously turned down ply material to be turned about a previously set bead pressed firmly into place. Such bladders are mounted on and supported by cylindrical support can assemblies or the like which may be indexed axially to and from the drum during the tire building process.
Most bladders used in dual bladder turn-up mechanisms are made of cord reinforced elastomeric material and include an annular outer wall portion, one or both axial ends of which are turned axially inwardly to form a pair of inner wall portions. The inner wall portions of each bladder terminate in annular mounting flanges which secure the bladder to the support can assembly. When installed, the flanges normally are offset to accommodate suitable air passages in the support can assembly for inflating the bladder. For an example of such a dual bladder turn-up mechanism, reference may be had to U.S. Pat. No. 3,560,301.
While such general type of bladders has been fairly satisfactory in performance, some problems exist in connection therewith. For example, the bladders may be securely locked in position during the turn-up operation; however, removal and replacement of the bladders heretofore has been a time consuming project. To mount the bladders, the support can assemblies have been of complicated construction usually requiring a plurality of mounting rings and plates which interfit in jigsaw puzzle-like manner to retain therebetween the bladder flanges. Moreover, proper placement and alignment of the bladder flanges has been difficult to obtain, and if misaligned, damage may result to the bladder. Also, desired circular expansion of the bladders often has been inhibited by the bladder and support can assembly constructions.
In an effort to eliminate the bladder flanges and complex means for mounting same, other types of bladders have been devised which are fully and continuously annularly molded. Such types of bladders have been provided with some form of mounting means such as integrally formed profiled mounting rings which fit in similarly profiled grooves in the support can assembly. An example of this type of bladder can be seen in U.S. Pat. No. 4,087,306. Other bladders have employed fittings or valves molded directly into the bladders to which air supply tubing may be connected. An example of this type of bladder can be seen in U.S. Pat. No. 3,305,427.
One drawback of these types of bladders is that the bladders are subject to distortion as the bladders are not securely locked or held to the support can assembly completely around its circumference. While the fittings or valves secure the bladder to the support can assembly at spaced-apart locations, the bladder is subject to serpentining, i.e., axial movement and/or lifting of the bladder from the support can assembly intermediately of the fittings, due to the substantial axial and radial shear forces developed during ply turn-up thereby destroying the uniform annular shape of the bladder as the same is expanded. Accordingly, uneven forces are applied to the folded ply edges which is undesirable. In addition, high bladder pressures required to obtain the desired forces acting to turn and stitch the tire plies result in high energy costs and short bladder life. Moreover, those bladders employing fittings or valves may be subject to early failure at the fittings or valves.
Regardless of the type of bladder employed, another drawback of many dual bladder turn-up mechanisms is the entanglement of hosing and cross-connections required to supply inflating air or other media to and from the bladders. Such plumbing connections unduly add to the complexity of the tire building machine and the cost thereof.
In view of the foregoing, it is a principal object of this invention to provide an improved bladder construction which eliminates many of the problems heretofore associated with known bladders and support can assemblies therefor. It is another object to provide an annular bladder support which mounts in a tire building machine as a complete assembly without internal tubing and cross-connections therefor. It is still another object to provide a dual bladder turn-up or like mechanism wherein the radially outer bladder achieves an essentially circular condition but for the radially inner bladder. Yet another object of the invention is to provide a bladder construction having improved rolling characteristics and which requires less air pressure to do the same amount of work thereby resulting in greater energy efficiency and longer bladder life.
It is a further principal object to provide an improved dual bladder turn-up for replacing existing turn-ups in new or retrofitted tire building machines of the type sold by applicant's assignee under the model designation "88 TBM".